1. Field of the Invention
The present invention relates to a valve comprised of a valve body incorporating a flow bore, of a closure element rotatably or pivotally adapted to said flow bore, said check element having the shape of a rotational body or part of one, incorporating flow ports and being supported by seat seals, and of a driving stem connected to said check element, whereby the stem is connected to the closure element by means of a driver element which is adapted to movably fit in a slot machined to the outside surface of the closure element, said slot being aligned orthogonal to the longitudinal axis of the flow port of the closure element. The valve is suited for checking or regulating the flow of a medium in a pipeline.
2. Description of the Related Art
The salient flow, regulating and checking characteristics of the ball valve are known in the art. Therefore, the use of this valve type is widespread and it is available in several different constructional embodiments. Ball valves developed for checking applications in particular conventionally have such a design in which the ball and the driving stem are fabricated as separate elements and in which the ball element is rotatably supported by means of seat seals adapted to the inlet and outlet sides of the valve body bore. The operating torque from the driving stem to the ball element is transmitted by a prismatic body, which is an integral part of the stem and has a cubic or rectangular shape to fit in a slot provided on the surface of the ball element, whereby the slot has matching dimensions and a straight or curved bottom. The play of the joint between the ball element and the stem is sufficiently large to allow unobstructed motion of the ball to enable pressure-assisted sealing of the valve, however, without sacrificing the torque-transmitting capability of the joint. The sealing force is created by the pressure differential prevailing between the valve ports, and consequently, when the ball element is rotated to the closed position the pressure pushes it against the seat seal.
The sides of the slot on the ball element surface are aligned orthogonal to the longitudinal axis of the flow port of the ball element, thus making the sides of the slot to be parallel with longitudinal axis of the flow bore of the valve in the closed position of the valve. In this fashion the closure element can move with respect to the stem end to rest against the seal. The bottom of the slot can also be curved in the direction of the slot's longitudinal axis.
The above-described joint between the ball element and the stem has been developed further by adapting a driver disc between the ball element and the stem having the purpose of aiding the motion of the ball element between the seat seals. The lower surface of the disc is provided with a straight ridge having a length equal to the disc diameter in a direction perpendicular to the longitudinal axis of the flow port of the ball element and the upper surface of the disc is correspondingly provided with a straight slot aligned orthogonally to the above-described ridge. The ridge of the lower surface is adapted to fit in the slot on the ball surface and a ridge formed to the end of the stem is adapted to fit in the slot of the disc's upper surface. As to its other functions, the valve corresponds to the sealing function of the first described embodiment of the stem joint, whereby the sealing force is also in this embodiment exerted by the pressure differential over the closed valve.
A further constructional embodiment used in ball valves is such in that the ball element surface has an internally splined hole into which a splined stem is fitted. The valve design may have one or two shafts supporting the ball, but the two-shaft type is more common. In the two-shaft construction the lower trunnion shaft below the ball element retains the ball centered relative to the driving shaft during operation of the valve, and the sealing function is provided by the pressure compressing the ball element against the seat seals. The function of the one-shaft valve corresponds to that of the above-described valves.
A typical stem-and-ball system designed for pressure-assisted sealing is disclosed in the U.S. Pat. No. 3,843,091 (Gachot, Oct. 22, 1974).
The U.S. Pat. No. 3,767,162 (Ohlsson, Oct. 23, 1973) concerns an invention related to the joint between the stem and the ball element.
The U.S. Pat. No. 4,342,330 (Wieveg et al., Aug. 8, 1982) discloses a design in which the joint between the ball element and the stem is implemented using a driver disc between the ball element and the stem.
The FI patent publication 79,253 (Kivipelto, Aug. 8, 1989) concerns an invention related to a one-shaft ball valve and employing a spline joint between the ball element and the shaft that transmits the operating torque.
Reliable function of the valve with a varying temperature of the flowing medium requires flexibility or play between the ball element and the seat seal in order to prevent the ball from jamming between the seals. When resilient seat seals made of plastic, for instance, are used, compensation of thermal expansion can be attained through elasticity of the seat seals. If the seat seals are made of a metallic material, a clearance is provided between the ball element and the seat seals so large that compressive contact of the ball element with both seat seals simultaneously is avoided.
During the rotation of the ball element to its closed position, its center point must shift in the direction of the flow so far from the center axis of the stem as required to eliminate the total play or half the elastic travel. The shift is necessary to achieve tightness of the valve. At the opening of the valve, the ball must correspondingly shift back by a corresponding distance toward the center axis of the stem under the thrust generated by the seat seal.
In conventional joints between the ball element and the stem, a problem is caused by the play in the joint between the stem and the ball element that is necessary for enabling the shift of the ball. During use the joint wears and its play increases in proportion to the operating cycles of the value, eventually resulting in annoying operating disturbance to the user. The increase of the play is accentuated by a high pressure difference imposed over the ball element. Wear is caused by the above-described reciprocating motion of the stem end in the slot of the ball surface during the operation of the valve.
This wear is especially severe in a valve with a metal seal. In such a valve the friction between the ball element and the seal is greater than in a valve with a resilient seal and the operating torque of the valve is higher. The higher torque in turn results in an increased pressure in the contacting areas of the stem joint with the ball, which further increases the frictional forces and hampers the return motion of the ball toward the center axis of the stem. This problem is avoided by virtue of the present invention. In prior-art methods the problem could have been overcome by using a ball element with two shafts, but such a construction is difficult to produce, expensive and prone to malfunction in comparison with the design offered by the present invention. The two-shaft construction necessitates the use of a movable seat seal which is compressed against the ball element by means of springs, for other mechanical or hydraulic elements in order to exert the sealing force.
The reciprocating motion of the ball causes wear and a subsequent increase of play in the joint between the ball and the stem, which in prior art has been simply circumvented through the adaptation of a driver disc in the above-described manner between the stem end and the ball, whereby the disc has a ridge and a slot for transmitting the operating torque from the stem to the ball element. This embodiment, however, must be provided with a clearance in the fits of the ridge and the slot on the opposite sides of the disc in order to attain a functioning pressure-assisted sealing effect, whereby the rotational play of the valve remains large and torque-transmitting capability of the stem minimal.
The embodiment based on the use of a driver disc removes the problem caused by the increase of play due to wear, but notwithstanding this, the play remains larger than that offered by the present invention because of the initial play necessary in such a construction. The slotted joints on the upper and lower surfaces of the disc must have play to allow the motion of the ball element even under a small pressure difference toward the direction of the flow when the valve is rotated closed. Correspondingly, the ball element must move easily back toward the center axis of the stem when the valve is opened. Moreover, when a slotted joint is used, the torque-transmitting capability of the joint remains inferior to a spline joint. To achieve a high torque-transmitting capability, the internal and external splines would have to be relatively high, which in its turn would necessitate a large diameter of one end of the stem. Herein, a problem arises in that the sealing area of the ball element is reduced and that a stem extended longer than normal cannot be adapted to the body without modification of the body structure. Reduction of the ball element area available for sealing necessitates the use of a larger-diameter ball element and possibly also increasing the size of the valve body. Consequently, the use of a larger-diameter stem may become very awkward. The use of an extended-length stem is necessary to maintain an appropriate operating temperature of the valve actuator and the stem seal when the medium flowing through the valve is extremely cold or hot, or in cases where, e.g., the stem seal must be modified for a drain tap necessary to collect a toxic medium. Of course, a similar adaptation problem is encountered when a driver element machined from the same blank with the stem is used.
The wear problem can also be overcome by using a ball element having a internally splined hole to accept the splined stem that rotates the ball element. Also such a design is incapable of achieving a ball element which is easily rotatable and can travel a large degree in the direction of the flow without resorting to the use of substantial play of the spline joint.
A large play in the joint between the ball element and the stem prevents the use of the valve as a regulating valve in most applications. Play in the operating control may also cause problems in closure valve use, because uncertainty in the positioning of the ball element to the optimally sealing position of the ball results in inferior check performance of the valve. These problems related to zero-play transmitting of the operating torque and increase of the operating play are overcome by virtue of the present iuvention.